Memory Modules

Two main types of industry-standard memory modules are used in laptops and portable computers today: SO-DIMM (small outline dual inline memory module) and Micro-DIMM (micro dual inline memory module). There are four main types of SO-DIMMs and two main types of Micro-DIMMs, with different sizes, speeds, and configurations available in each type (see Table 6.6). The SO-DIMM and Micro-DIMM form factors and pinouts are JEDEC standards, which means that they are industry standards, thus ensuring conformity , compatibility, and interchangeability among different systems and manufacturers.

Table 6.6. Laptop/Portable Memory Module Types

Number of Pins	Module Type	Data Width	Memory Type
72	SO-DIMM	32 bits	FPM/EDO
144	SO-DIMM	64 bits	FPM/EDO
144	SO-DIMM	64 bits	SDRAM
200	SO-DIMM	64 bits	DDR SDRAM
144	Micro-DIMM	64 bits	SDRAM
172	Micro-DIMM	64 bits	DDR SDRAM

SO-DIMMs are mainly used by laptop or notebook computers, whereas the smaller Micro-DIMMs are used mainly by subnotebooks, PDAs, and palmtop computers.

SO-DIMMs

Most laptop and notebook computers use SO-DIMMs (small outline dual inline memory modules), which are basically smaller and more compact modules than the standard DIMMs used in desktop systems. Although they differ in form factor and pinout, as compared to standard DIMMs, SO-DIMMs perform the same function. They allow for easy, modular memory installations and upgrades. The modules are inserted into sockets in the system and can easily be installed or removed. As the name implies, SO-DIMMs have different pins on each side of the module, with the odd-numbered pins on the front and the even-numbered pins on the back. Special keying notches on either side allow the module to be inserted into the connector only in the proper orientation. The notches are normally offset in their space for voltage keying as well. A variety of SO-DIMMs are available for different system requirements. Because they are not all interchangeable, it is necessary to ensure you match the correct type for a given system.

72-pin SO-DIMM

The 72-pin SO-DIMM is an older type used primarily in older 486 class portables. The 72-pin SO-DIMM reads and writes data 32 bits (4 bytes) at a time, which is a perfect match for 32-bit 486 processors. These modules are largely obsolete and are not used in any new system designs. They are still available for upgrading older systems, but because the supply is dwindling, the prices are higher than for newer , more modern modules.

The 72-pin SO-DIMMs have the industry-standard form factor shown in the Figure 6.1.

The 72-pin SO-DIMMs are available in several versions, with capacities of up to 64MB. Most utilize FPM/EDO memory chips, which are rated 60ns for speed and run on 3.3 volts . The most common sizes, including the depths and widths of the modules, are shown in Table 6.7.

Table 6.7. 72-pin SO-DIMM Module Capacities

Capacity	(Depth x Width)
4MB	(1M x 32b)
8MB	(2M x 32b)
16MB	(4M x 32b)
32MB	(8M x 32b)
64MB	(16M x 32b)

The 72-pin modules have a 32-bit-wide data bus, which is equal to 4 bytes. For example, a 64MB 72-pin SO-DIMM is arranged internally as 16 million rows, with 32 bits (4 bytes) in each row, for a total of 64 million (16 million x 4) bytes.

The JEDEC standard pinout for 72-pin SO-DIMMs is listed in Tables 6.8 and 6.9.

Table 6.8. 72-pin SO-DIMM Pinout (Front)

Pin	Signal	Pin	Signal	Pin	Signal	Pin	Signal
1	VSS	19	A10	37	DQ16	55	NC
3	DQ1	21	DQ8	39	VSS	57	DQ25
5	DQ3	23	DQ10	41	CAS2#	59	DQ28
7	DQ5	25	DQ12	43	CAS1#	61	VDD
9	DQ7	27	DQ14	45	RAS1#	63	DQ30
11	PRD1	29	A11	47	WE#	65	NC
13	A1	31	A8	49	DQ18	67	PRD3
15	A3	33	RAS3#	51	DQ20	69	PRD5
17	A5	35	DQ15	53	DQ22	71	PRD7

Table 6.9. 72-pin SO-DIMM Pinout (Back)

Pin	Signal	Pin	Signal	Pin	Signal	Pin	Signal
2	DQ0	20	NC	38	DQ17	56	DQ24
4	DQ2	22	DQ9	40	CAS0#	58	DQ26
6	DQ4	24	DQ11	42	CAS3#	60	DQ27
8	DQ6	26	DQ13	44	RAS0#	62	DQ29
10	VDD	28	A7	46	A12	64	DQ31
12	A0	30	VDD	48	A13	66	PRD2
14	A2	32	A9	50	DQ19	68	PRD4
16	A4	34	RAS2#	52	DQ21	70	PRD6
18	A6	36	NC	54	DQ23	72	VSS

All SO-DIMM contacts are normally gold plated and should match the plating on the mating connector for reliable operation. You should avoid modules with tin-plated contacts because tin will react with the gold plating on the connector contacts, causing corrosion and eventual memory failures.

144-pin SO-DIMM

The 144-pin SO-DIMMs are very popular in Pentium or Athlon class and newer laptop and notebook computers. They can read or write data 64 bits at a time, which makes them a perfect match for 64-bit processors such as the Pentium and newer chips. The 144-pin SO-DIMMs are available in several different memory chip types, including EDO, 66MHz SDRAM, PC100 SDRAM, and PC133 SDRAM versions. The 144-pin SO-DIMMs are not available in versions supporting ECC (error-correction code).

When installing these modules, you must ensure that the type you are using matches the requirements of the system. In most cases, you can put a faster module in place of a slower one, but only if it is the same basic memory type. For example, you can usually install PC133 memory even if the system only requires PC100 or even 66MHz SDRAM, but you cannot use SDRAM modules in systems that require EDO, or vice versa. Also, you should not install modules that are slower than the system requires, even if they are the correct memory type.

The speeds of 144-pin SO-DIMMs are rated as shown in Table 6.10.

Table 6.10. 144-pin SDRAM SO-DIMM Speeds

Module Type	Cycle Time	Module Frequency	Module Width	Module Bandwidth
PC66	10.0ns	66MHz	8 bytes	533MBps
PC100	8.0ns	100MHz	8 bytes	800MBps
PC133	7.5ns	133MHz	8 bytes	1,066MBps

The throughput or bandwidth is simply the frequency multiplied by the width, which gives the rate at which data can be read from or written to the module.

Another specification to consider that is related to speed is the CAS (column address strobe) Latency , often abbreviated as CL . This is also sometimes called read latency , and it's the number of clock cycles occurring between the registration of the CAS signal and the resultant output data, with lower numbers of cycles indicating faster (better) performance. Typically you find SDRAM modules rated CL 2 or CL 3. If possible, choose modules with a lower CL figure, because the motherboard chipset will read that specification out of the SPD (serial presence detect) ROM on the module and switch to slightly faster cycling rates.

The 144-pin SO-DIMMs have the industry-standard form factor shown in the Figure 6.2.

All 144-pin SO-DIMMs have the odd-numbered pins (1 “143) on the front and even-numbered pins (2 “144) on the back and are 2.66'' (67.6mm) long. The number of actual chips on the modules can vary, as can the physical height of the module. The modules are normally either 1'' (25.4mm) or 1.25'' (31.75mm) high, although the heights may vary slightly.

The 144-pin SO-DIMMs use a SPD ROM (read-only memory) onboard, which the motherboard reads to determine the exact specifications of the modules installed. The ROM is normally a small chip on the module and can be seen as component "U1" in the preceding figure.

The modules are keyed via a small notch in the connector area on the bottom (seen between pins 59 and 61 on the front), which prevents them from being installed backward and provides voltage keying as well. The voltage keying is shown Figure 6.3.

Figure 6.3. 144-pin SO-DIMM voltage keying.

Although the standard allowed for 5V modules, currently all 144-pin SO-DIMMs have the notch in the center position, indicating 3.3V operation. All the systems I am aware of will only accept 3.3V 144-pin modules, which draw less power and generate less heat.

The 144-pin SO-DIMMs are available in several versions, with capacities of up to 512MB. They can utilize either EDO (extended data out) memory chips or SDRAM (synchronous dynamic RAM) at several different rated speeds. The most common sizes are shown in Table 6.11.

Table 6.11. 144-pin SO-DIMM Module Capacities

Capacity	(Depth x Width)
32MB	(4M x 64b)
64MB	(8M x 64b)
128MB	(16M x 64b)
256MB	(32M x 64b)
512MB	(64M x 64b)

The capacity can be determined by multiplying the depth by the width. The 144-pin modules have a 64-bit-wide data bus, which is equal to 8 bytes. For example, a 512MB 144-pin SO-DIMM is arranged internally as 64 million rows, with 64 bits (8 bytes) in each row, for a total of 512 million (64 million x 8) bytes.

The JEDEC standard pinout for 144-pin SO-DIMMs using FPM or EDO RAM are listed in Tables 6.12 and 6.13.

Table 6.12. 144-pin EDO/FPM SO-DIMM Pinout (Front)

Pin	Signal	Pin	Signal	Pin	Signal	Pin	Signal
1	VSS	37	DQ8	73	OE#	109	A9
3	DQ0	39	DQ9	75	VSS	111	A10
5	DQ1	41	DQ10	77	NC	113	VDD
7	DQ2	43	DQ11	79	NC	115	CAS2#
9	DQ3	45	VDD	81	VDD	117	CAS3#
11	VDD	47	DQ12	83	DQ16	119	VSS
13	DQ4	49	DQ13	85	DQ17	121	DQ24
15	DQ5	51	DQ14	87	DQ18	123	DQ25
17	DQ6	53	DQ15	89	DQ19	125	DQ26
19	DQ7	55	VSS	91	VSS	127	DQ27
21	VSS	57	NC	93	DQ20	129	VDD
23	CAS0#	59	NC	95	DQ21	131	DQ28
25	CAS1#	61	NC	97	DQ22	133	DQ29
27	VDD	63	VDD	99	DQ23	135	DQ30
29	A0	65	NC	101	VDD	137	DQ31
31	A1	67	WE#	103	A6	139	VSS
33	A2	69	RAS0#	105	A8	141	SDA
35	VSS	71	NC	107	VSS	143	VDD

Table 6.13. 144-pin EDO/FPM SO-DIMM Pinout (Back)

Pin	Signal	Pin	Signal	Pin	Signal	Pin	Signal
2	VSS	38	DQ40	74	NC	110	A12
4	DQ32	40	DQ41	76	VSS	112	A13
6	DQ33	42	DQ42	78	NC	114	VDD
8	DQ34	44	DQ43	80	NC	116	CAS6#
10	DQ35	46	VDD	82	VDD	118	CAS7#
12	VDD	48	DQ44	84	DQ48	120	VSS
14	DQ36	50	DQ45	86	DQ49	122	DQ56
16	DQ37	52	DQ46	88	DQ50	124	DQ57
18	DQ38	54	DQ47	90	DQ51	126	DQ58
20	DQ39	56	VSS	92	VSS	128	DQ59
22	VSS	58	NC	94	DQ52	130	VDD
24	CAS4#	60	NC	96	DQ53	132	DQ60
26	CAS5#	62	NC	98	DQ54	134	DQ61
28	VDD	64	VDD	100	DQ55	136	DQ62
30	A3	66	NC	102	VDD	138	DQ63
32	A4	68	NC	104	A7	140	VSS
34	A5	70	NC	106	A11	142	SCL
36	VSS	72	NC	108	VSS	144	VDD

The JEDEC standard pinout for 144-pin SO-DIMMs using SDRAM are listed in Tables 6.14 and 6.15.

Table 6.14. 144-pin SDRAM SO-DIMM Pinout (Front)

Pin	Signal	Pin	Signal	Pin	Signal	Pin	Signal
1	VSS	37	DQ8	73	NC	109	A9
3	DQ0	39	DQ9	75	VSS	111	A10
5	DQ1	41	DQ10	77	NC	113	VDD
7	DQ2	43	DQ11	79	NC	115	DQMB2
9	DQ3	45	VDD	81	VDD	117	DQMB3
11	VDD	47	DQ12	83	DQ16	119	VSS
13	DQ4	49	DQ13	85	DQ17	121	DQ24
15	DQ5	51	DQ14	87	DQ18	123	DQ25
17	DQ6	53	DQ15	89	DQ19	125	DQ26
19	DQ7	55	VSS	91	VSS	127	DQ27
21	VSS	57	NC	93	DQ20	129	VDD
23	DQMB0	59	NC	95	DQ21	131	DQ28
25	DQMB1	61	CK0	97	DQ22	133	DQ29
27	VDD	63	VDD	99	DQ23	135	DQ30
29	A0	65	RAS#	101	VDD	137	DQ31
31	A1	67	WE#	103	A6	139	VSS
33	A2	69	S0#	105	A8	141	SDA
35	VSS	71	S1#	107	VSS	143	VDD

Table 6.15. 144-pin SDRAM SO-DIMM Pinout (Back)

Pin	Signal	Pin	Signal	Pin	Signal	Pin	Signal
2	VSS	38	DQ40	74	CK1	110	BA1
4	DQ32	40	DQ41	76	VSS	112	A11
6	DQ33	42	DQ42	78	NC	114	VDD
8	DQ34	44	DQ43	80	NC	116	DQMB6
10	DQ35	46	VDD	82	VDD	118	DQMB7
12	VDD	48	DQ44	84	DQ48	120	VSS
14	DQ36	50	DQ45	86	DQ49	122	DQ56
16	DQ37	52	DQ46	88	DQ50	124	DQ57
18	DQ38	54	DQ47	90	DQ51	126	DQ58
20	DQ39	56	VSS	92	VSS	128	DQ59
22	VSS	58	NC	94	DQ52	130	VDD
24	DQMB4	60	NC	96	DQ53	132	DQ60
26	DQMB5	62	CKE0	98	DQ54	134	DQ61
28	VDD	64	VDD	100	DQ55	136	DQ62
30	A3	66	CAS#	102	VDD	138	DQ63
32	A4	68	CKE1	104	A7	140	VSS
34	A5	70	A12	106	BA0	142	SCL
36	VSS	72	NC	108	VSS	144	VDD

All DIMM contacts are normally gold plated and should match the plating on the mating connector for reliable operation.

200-pin SO-DIMM

The 200-pin SO-DIMMs are used to provide DDR (double data rate) SDRAM (synchronous dynamic RAM) memory for laptop computers. DDR SDRAM is the type of memory used by most of the recent high-performance laptops. They normally run on only 2.5 volts, making them very efficient for longer battery life. Each 200-pin SO-DIMM incorporates a 64-bit data path , which is ideal because they can be installed individually in 64-bit (Pentium and newer) systems. The 200-pin SO-DIMMs are available in PC1600 (200MHz), PC2100 (266MHz), and PC2700 (333MHz) DDR SDRAM versions. They are also available in versions supporting ECC (error-correction code), which offers 1-bit error detection and correction for greater integrity. ECC requires support from the chipset and motherboard.

When installing these modules you must ensure the type you are using matches the requirements of the system. In most cases, you can put a faster module in place of a slower one, but only if it is the same basic memory type. For example, you can usually install PC2700 memory, even if the system only requires PC2100 or even PC1600, but you cannot use modules that are slower than the system requires.

The speeds of 200-pin SO-DIMMs are rated as shown in Table 6.16.

Table 6.16. 200-pin DDR SDRAM SO-DIMM Speeds

Module Type	Cycle Time	Frequency SDR/ DDR	Module Width	Module Bandwidth
PC2700	6.0ns	166/333MHz	8 bytes	2,666MBps
PC2100	7.5ns	133/266MHz	8 bytes	2,133MBps
PC1600	10.0ns	100/200MHz	8 bytes	1,600MBps

The cycle time in nanoseconds (billionths of a second) matches the single data rate (SDR) clock speed, but double data rate (DDR) modules transfer twice per cycle, so the DDR frequency is always equal to double the SDR frequency. The throughput or bandwidth is simply the DDR frequency times the width, which gives the rate at which data can be read from or written to the module.

Another specification to consider that is related to speed is the CAS (column address strobe) Latency , often abbreviated as CL . This is also sometimes called read latency , and it's the number of clock cycles occurring between the registration of the CAS signal and the resultant output data, with lower numbers of cycles indicating faster (better) performance. Typically you can find DDR SDRAM modules rated CL 2 or CL 2.5. If possible, choose modules with a lower CL figure, because the motherboard chipset will read that specification out of the SPD (serial presence detect) ROM on the module and switch to slightly faster cycling rates.

The 200-pin SO-DIMMs have the JEDEC industry-standard form factor shown in Figure 6.4.

Figure 6.4. 200-pin DDR SDRAM SO-DIMM.

All 200-pin SO-DIMMs have the odd-numbered pins (1 “199) on the front and even-numbered pins (2 “200) on the back and are 2.66'' (67.6mm) long. The number of actual chips on the module can vary, as can the physical height of the module. The modules are normally either 1'' (25.4mm) or 1.25'' (31.75mm) high, although some versions can be up to 1.5'' (38.1mm) high (the heights may vary slightly). The taller modules may not fit in all systems, so be sure to check before ordering.

Although the 200-pin modules are the same physical size as 144-pin modules, the pin spacing is tighter and the notch is offset much farther to the left, preventing the installation of 200-pin modules in 144-pin sockets, and vice versa.

The 200-pin SO-DIMMs use a SPD ROM (read-only memory) onboard, which the motherboard reads to determine the exact specifications of the modules installed. The ROM is normally a small chip on the module, much smaller than the memory chips, and may be mounted on the front or back side. The SPD chip can be seen as component "U9" in Figure 6.4.

The modules are keyed via a small notch in the connector area on the bottom (seen between pins 39 and 41 on the front), which prevents them from being installed backward and provides voltage keying as well. The voltage keying is shown in Figure 6.5.

Figure 6.5. 200-pin SO-DIMM voltage keying.

Although the standard allows for 1.5V modules, currently most systems use 200-pin SO-DIMMs with the notch in the left position, indicating 2.5V operation. Regardless of the voltage used, the notch prevents plugging in modules of the improper voltage into a given system.

The 200-pin SO-DIMMs are available in several versions, with capacities of up to 1GB. They utilize DDR SDRAM at several different rated speeds. The most common capacities are shown in Table 6.17.

Table 6.17. 200-pin SO-DIMM Module Capacities

Capacity	(Depth x Width )
32MB	(4M x 64b)
64MB	(8M x 64b)
128MB	(16M x 64b)
256MB	(32M x 64b)
512MB	(64M x 64b)
1GB	(128M x 64b)

The capacity can be determined by multiplying the depth by the width. The 200-pin modules have a 64-bit-wide data bus, which is equal to 8 bytes. For example, a 1GB 200-pin SO-DIMM is arranged internally as 128 million rows, with 64 bits (8 bytes) in each row. If you multiply 128 million by 8, you get 1,024 million bytes, or 1GB.

The JEDEC standard pinout and pin descriptions for 200-pin SO-DIMMs are listed in Tables 6.18 and 6.19.

Table 6.18. 200-pin DDR SDRAM SO-DIMM Pinout (Front)

Pin	Signal	Pin	Signal	Pin	Signal	Pin	Signal
1	VREF	51	VSS	101	A9	151	DQ42
3	VSS	53	DQ19	103	VSS	153	DQ43
5	DQ0	55	DQ24	105	A7	155	VDD
7	DQ1	57	VDD	107	A5	157	VDD
9	VDD	59	DQ25	109	A3	159	VSS
11	DQS0	61	DQS3	111	A1	161	VSS
13	DQ2	63	VSS	113	VDD	163	DQ48
15	VSS	65	DQ26	115	A10	165	DQ49
17	DQ3	67	DQ27	117	BA0	167	VDD
19	DQ8	69	VDD	119	WE#	169	DQS6
21	VDD	71	CB0	121	S0#	171	DQ50
23	DQ9	73	CB1	123	A13	173	VSS
25	DQS1	75	VSS	125	VSS	175	DQ51
27	VSS	77	DQS8	127	DQ32	177	DQ56
29	DQ10	79	CB2	129	DQ33	179	VDD
31	DQ11	81	VDD	131	VDD	181	DQ57
33	VDD	83	CB3	133	DQS4	183	DQS7
35	CK0	85	NC	135	DQ34	185	VSS
37	CK0#	87	VSS	137	VSS	187	DQ58
39	VSS	89	CK2	139	DQ35	189	DQ59
41	DQ16	91	CK2#	141	DQ40	191	VDD
43	DQ17	93	VDD	143	VDD	193	SDA
45	VDD	95	CKE1	145	DQ41	195	SCL
47	DQS2	97	NC	147	DQS5	197	VDDSPD
49	DQ18	99	A12	149	VSS	199	VDDID
See table 6.20 for pin descriptions.

Table 6.19. 200-pin DDR SDRAM SO-DIMM Pinout (Back)

Pin	Signal	Pin	Signal	Pin	Signal	Pin	Signal
2	VREF	52	VSS	102	A8	152	DQ46
4	VSS	54	DQ23	104	VSS	154	DQ47
6	DQ4	56	DQ28	106	A6	156	VDD
8	DQ5	58	VDD	108	A4	158	CK1#
10	VDD	60	DQ29	110	A2	160	CK1
12	DM0	62	DM3	112	A0	162	VSS
14	DQ6	64	VSS	114	VDD	164	DQ52
16	VSS	66	DQ30	116	BA1	166	DQ53
18	DQ7	68	DQ31	118	RAS#	168	VDD
20	DQ12	70	VDD	120	CAS#	170	DM6
22	VDD	72	CB4	122	S1#	172	DQ54
24	DQ13	74	CB5	124	NC	174	VSS
26	DM1	76	VSS	126	VSS	176	DQ55
28	VSS	78	DM8	128	DQ36	178	DQ60
30	DQ14	80	CB6	130	DQ37	180	VDD
32	DQ15	82	VDD	132	VDD	182	DQ61
34	VDD	84	CB7	134	DM4	184	DM7
36	VDD	86	NC	136	DQ38	186	VSS
38	VSS	88	VSS	138	VSS	188	DQ62
40	VSS	90	VSS	140	DQ39	190	DQ63
42	DQ20	92	VDD	142	DQ44	192	VDD
44	DQ21	94	VDD	144	VDD	194	SA0
46	VDD	96	CKE0	146	DQ45	196	SA1
48	DM2	98	NC	148	DM5	198	SA2
50	DQ22	100	A11	150	VSS	200	NC
See table 6.20 for pin descriptions.

All DIMM contacts are normally gold plated and should match the plating on the mating connector for reliable operation.

Table 6.20 describes the pin functions.

Table 6.20. 200-pin DDR SDRAM SO-DIMM Pin Descriptions

Signal	Description	Number of pins
A(0:9,11:13)	Address Inputs	13
A10/AP	Address Input/AutoPrecharge	1
BA(0:1)	SDRAM Bank Address	2
CAS#	Column Address Strobe (Active Low)	1
CB(7:0)	Data Check Bits Input/Output	8
CK(0:2)	Clock Inputs, Positive Line	3
CK(0:2)#	Clock Inputs, Negative Line	3
CKE(0:1)	Clock Enables	2
DM(0:8)	Data Masks	9
DQ(0:63)	Data Input/Output	64
DQS(0:8)	Data Strobes	9
NC	Not Connected (Reserved)	6
RAS#	Row Address Strobe (Active Low)	1
S(0:1)#	Chip Selects (Active Low)	2
SA(0:2)	SPD Address	3
SCL	SPD Clock Input	1
SDA	SPD Data Input/Output	1
VDD	Core and I/O Power	33
VDDID	VDD, VDDQ Level Detection	1
VDDSPD	Serial Presence Detect (SPD) Power	1
VREF	Input/Output Reference	2
VSS	Ground	33
WE#	Write Enable (Active Low)	1

Micro-DIMMs

Micro-DIMMs (micro dual inline memory modules) are a newer and smaller type of memory module used mainly in subnotebooks, PDAs, and palmtop computers. As with all DIMMs, they have pins on both sides that perform different functions. The two main types of Micro-DIMMs are 144-pin and 172-pin. The 144-pin versions contain SDRAM (synchronous dynamic RAM) and are similar to 144-pin SO-DIMMs, whereas the 172-pin versions contain DDR (double data rate) SDRAM and are similar to 200-pin SO-DIMMs. The Micro-DIMMs are about half the size of the SO-DIMMs and yet offer similar capacities and performance.

144-pin SDRAM Micro-DIMM

The 144-pin SDRAM Micro-DIMMs are similar to the 144-pin SDRAM SO-DIMMs, but they're made to about half the physical size so as to fit the very tight form factors of smaller systems. Other than size, they have the same specifications as the 144-pin SDRAM SO-DIMMs, including the following features:

• JEDEC-standard form factor and pinout

• 64-bit (8 byte) data bus

• Single data rate SDRAM

• PC100 (100MHz) and PC133 (133MHz) operation

• 3.3V power

• Serial presence detect (SPD)

The 144-pin SDRAM Micro-DIMMs are only 1.5'' (38mm) long and 1.18'' (30mm) high, which is about half the size of an equivalent SO-DIMM. Unlike SO-DIMMs, Micro-DIMMs do not have any notches in the connector pin area; however, a notch is used on the left side to ensure proper insertion. They also have a unique size that is not interchangeable with other modules.

The 144-pin SDRAM Micro-DIMMs are available in PC100 and PC133 speeds. You can generally use PC133 modules in place of PC100 modules, but not the other way around. The speeds of 144-pin Micro-DIMMs are rated as shown in Table 6.21.

Table 6.21. 144-pin SDRAM Micro-DIMM Speeds

Module Type	Cycle Time	Module Frequency	Module Width	Module Bandwidth
PC100	8.0ns	100MHz	8 bytes	800MBps
PC133	7.5ns	133MHz	8 bytes	1,066MBps

The throughput or bandwidth is simply the frequency times the width, which gives the rate at which data can be read from or written to the module.

As with SDRAM SO-DIMMs, another performance specification to consider that is related to speed is the CAS (column address strobe) Latency , often abbreviated as CL . Typically you find SDRAM modules rated CL 2 or CL 3. If possible, choose modules with a lower CL figure, because the motherboard chipset will read that specification out of the SPD ROM on the module and switch to slightly faster cycling rates.

The 144-pin SDRAM Micro-DIMMs have the industry-standard form factor shown in Figure 6.6.

Figure 6.6. 144-pin SDRAM Micro-DIMM.

All 144-pin Micro-DIMMs have the odd-numbered pins (1 “143) on the front and even-numbered pins (2 “144) on the back and are 1.5'' (38mm) long and 1.18'' (30mm) high. The number of actual chips on the modules can vary.

The 144-pin Micro-DIMMs use an SPD ROM onboard, which the motherboard reads to determine the exact specifications of the modules installed. The ROM is normally a small chip on the module and can be seen as the smaller component "U5" in the preceding figure.

The modules are keyed via a small notch on the left side of the connector area, which prevents them from being installed backward.

The 144-pin Micro-DIMMs are available in several versions, with capacities of up to 256MB. The most common sizes are shown Table 6.22.

Table 6.22. 144-pin SDRAM Micro-DIMM Module Capacities

Capacity	(Depth x Width )
64MB	(8M x 64b)
128MB	(16M x 64b)
256MB	(32M x 64b)

The capacity can be determined by multiplying the depth by the width. The 144-pin modules have a 64-bit-wide data bus, which is equal to 8 bytes. For example, a 256MB Micro-DIMM is arranged internally as 32 million rows, with 64 bits (8 bytes) in each row, for a total of 256 million (32 million x 8) bytes.

The JEDEC standard pinout for 144-pin SDRAM Micro-DIMMs is listed in Tables 6.23 and 6.24.

Table 6.23. 144-pin SDRAM Micro-DIMM Pinout (Front)

Pin	Signal	Pin	Signal	Pin	Signal	Pin	Signal
1	VSS	37	DQ8	73	NC	109	A9
3	DQ0	39	DQ9	75	VSS	111	A10
5	DQ1	41	DQ10	77	NC	113	VDD
7	DQ2	43	DQ11	79	NC	115	DQM2
9	DQ3	45	VDD	81	VDD	117	DQM3
11	VDD	47	DQ12	83	DQ16	119	VSS
13	DQ4	49	DQ13	85	DQ17	121	DQ24
15	DQ5	51	DQ14	87	DQ18	123	DQ25
17	DQ6	53	DQ15	89	DQ19	125	DQ26
19	DQ7	55	VSS	91	VSS	127	DQ27
21	VSS	57	NC	93	DQ20	129	VDD
23	DQM0	59	NC	95	DQ21	131	DQ28
25	DQM1	61	CK0	97	DQ22	133	DQ29
27	VDD	63	VDD	99	DQ23	135	DQ30
29	A0	65	RAS#	101	VDD	137	DQ31
31	A1	67	WE#	103	A6	139	VSS
33	A2	69	S0#	105	A8	141	SDA
35	VSS	71	NC	107	VSS	143	VDD

Table 6.24. 144-pin SDRAM Micro-DIMM Pinout (Back)

Pin	Signal	Pin	Signal	Pin	Signal	Pin	Signal
2	VSS	38	DQ40	74	NC	110	BA1
4	DQ32	40	DQ41	76	VSS	112	A11
6	DQ33	42	DQ42	78	NC	114	VDD
8	DQ34	44	DQ43	80	NC	116	DQM6
10	DQ35	46	VDD	82	VDD	118	DQM7
12	VDD	48	DQ44	84	DQ48	120	VSS
14	DQ36	50	DQ45	86	DQ49	122	DQ56
16	DQ37	52	DQ46	88	DQ50	124	DQ57
18	DQ38	54	DQ47	90	DQ51	126	DQ58
20	DQ39	56	VSS	92	VSS	128	DQ59
22	VSS	58	NC	94	DQ52	130	VDD
24	DQM4	60	NC	96	DQ53	132	DQ60
26	DQM5	62	CKE0	98	DQ54	134	DQ61
28	VDD	64	VDD	100	DQ55	136	DQ62
30	A3	66	CAS#	102	VDD	138	DQ63
32	A4	68	NC	104	A7	140	VSS
34	A5	70	A12	106	BA0	142	SCL
36	VSS	72	NC	108	VSS	144	VDD

All DIMM contacts are normally gold plated and should match the plating on the mating connector for reliable operation.

172-pin DDR SDRAM Micro-DIMM

The 172-pin DDR SDRAM Micro-DIMMs are similar to the 200-pin DDR SDRAM SO-DIMMs, but they're about half the physical size so as to fit the very tight form factors of smaller systems. Other than that, they have the same specifications as the 200-pin DDR SDRAM SO-DIMMs, including the following features:

• JEDEC-standard form factor and pinout

• 64-bit (8 byte) data bus

• DDR (double data rate) SDRAM

• PC1600 (200MHz), PC2100 (266MHz), and PC2700 (333MHz) operation

• 2.5V power

• Serial presence detect (SPD)

The 172-pin DDR SDRAM Micro-DIMMs are only 1.8'' (45.5mm) long and 1.18'' (30mm) high, which is about half the size of an equivalent SO-DIMM. Unlike SO-DIMMs, Micro-DIMMs do not have any notches in the connector pin area; however, a notch is used on the left side to ensure proper insertion. They also have a unique size that is not interchangeable with other modules. Unlike the DDR SO-DIMMs, DDR Micro-DIMMs do not support ECC (error-correcting code) functions.

The 144-pin SDRAM Micro-DIMMs are available in PC1600, PC2100, and PC2700 speeds. You can generally use faster modules in place of slower modules, but not the other way around. The speeds of 172-pin DDR SDRAM Micro-DIMMs are rated as shown in Table 6.25.

Table 6.25. 172-pin DDR SDRAM Micro-DIMM Speeds

Module Type	Cycle Time	Frequency SDR/ DDR	Module Width	Module Bandwidth
PC2700	6.0ns	166/333MHz	8 bytes	2,666MBps
PC2100	7.5ns	133/266MHz	8 bytes	2,133MBps
PC1600	10.0ns	100/200MHz	8 bytes	1,600MBps

The cycle time in nanoseconds (billionths of a second) matches the single data rate (SDR) clock speed, but double data rate (DDR) modules transfer twice per cycle, so the DDR frequency is always double the SDR frequency. The throughput or bandwidth is simply the DDR frequency times the width, which gives the rate at which data can be read from or written to the module.

As with DDR SDRAM SO-DIMMs, another performance specification to consider that is related to speed is the CAS (column address strobe) Latency , often abbreviated as CL . Typically you find SDRAM modules rated CL 2 or CL 2.5. If possible, choose modules with a lower CL figure, because the motherboard chipset will read that specification out of the SPD ROM on the module and switch to slightly faster cycling rates.

The 172-pin SDRAM Micro-DIMMs have the industry-standard form factor shown in Figure 6.7.

Figure 6.7. 172-pin DDR SDRAM Micro-DIMM.

All 172-pin DDR SDRAM Micro-DIMMs have the odd-numbered pins (1 “171) on the front and even numbered pins (2 “172) on the back and are 1.8'' (45.5mm) long and 1.18'' (30mm) high. The number of actual chips on the modules can vary.

The 172-pin DDR SDRAM Micro-DIMMs use an SPD ROM onboard, which the motherboard reads to determine the exact specifications of the modules installed. The ROM is normally a small chip on the module.

The modules are keyed via a small notch on the left side of the connector area, which prevents them from being installed backward.

The 172-pin DDR SDRAM Micro-DIMMs are available in several versions, with capacities of up to 256MB. The most common sizes are shown in Table 6.26.

Table 6.26. 172-pin DDR SDRAM Micro-DIMM Module Capacities

Capacity	(Depth x Width )
64MB	(8M x 64b)
128MB	(16M x 64b)
256MB	(32M x 64b)

The capacity can be determined by multiplying the depth by the width. The 172-pin modules have a 64-bit-wide data bus, which is equal to 8 bytes. For example, a 256MB Micro-DIMM is arranged internally as 32 million rows, with 64 bits (8 bytes) in each row, for a total of 256 million (32 million x 8) bytes.

The JEDEC standard pinouts for 172-pin SDRAM Micro-DIMMs are listed in Tables 6.27 and 6.28.

Table 6.27. 172-pin DDR SDRAM Micro-DIMM Pinout (Front)

Pin	Signal	Pin	Signal	Pin	Signal	Pin	Signal
2	VREF	46	VDD	88	BA1	132	CK1#
4	VSS	48	DM2	90	VDD	134	CK1
6	DQ4	50	DQ22	92	RAS#	136	VSS
8	DQ5	52	VSS	94	CAS#	138	DQ52
10	VDD	54	DQ23	96	NC	140	DQ53
12	DM0	56	DQ28	98	NC	142	VDD
14	DQ6	58	VDD	100	VSS	144	DM6
16	VSS	60	DQ29	102	DQ36	146	DQ54
18	DQ7	62	DM3	104	DQ37	148	VSS
20	DQ12	64	VSS	106	VDD	150	DQ55
22	VDD	66	DQ30	108	DM4	152	DQ60
24	DQ13	68	DQ31	110	DQ38	154	VDD
26	DM1	70	VDD	112	VSS	156	DQ61
28	VSS	72	CKE0	114	DQ39	158	DM7
30	DQ14	74	A11	116	DQ44	160	VSS
32	DQ15	76	A8	118	VDD	162	DQ62
34	VDD	78	A6	120	DQ45	164	DQ63
36	VDD	80	VSS	122	DM5	166	VDD
38	VSS	82	A4	124	VSS	168	SA0
40	VSS	84	A2	126	DQ46	170	SA1
42	DQ20	86	A0	128	DQ47	172	SA2
44	DQ21			130	VDD

Table 6.28. 172-pin DDR SDRAM Micro-DIMM Pinout (Back)

Pin	Signal	Pin	Signal	Pin	Signal	Pin	Signal
1	VREF	45	VDD	87	A10/AP	131	VDD
3	VSS	47	DQS2	89	VDD	133	VSS
5	DQ0	49	DQ18	91	BA0	135	VSS
7	DQ1	51	VSS	93	WE#	137	DQ48
9	VDD	53	DQ19	95	S0#	139	DQ49
11	DQS0	55	DQ24	97	NC	141	VDD
13	DQ2	57	VDD	99	VSS	143	DQS6
15	VSS	59	DQ25	101	DQ32	145	DQ50
17	DQ3	61	DQS3	103	DQ33	147	VSS
19	DQ8	63	VSS	105	VDD	149	DQ51
21	VDD	65	DQ26	107	DQS4	151	DQ56
23	DQ9	67	DQ27	109	DQ34	153	VDD
25	DQS1	69	VDD	111	VSS	155	DQ57
27	VSS	71	NC	113	DQ35	157	DQS7
29	DQ10	73	A12	115	DQ40	159	VSS
31	DQ11	75	A9	117	VDD	161	DQ58
33	VDD	77	A7	119	DQ41	163	DQ59
35	CK0	79	VSS	121	DQS5	165	VDD
37	CK0#	81	A5	123	VSS	167	SDA
39	VSS	83	A3	125	DQ42	169	SCL
41	DQ16	85	A1	127	DQ43	171	VDDSPD
43	DQ17			129	VDD

All DIMM contacts are normally gold plated and should match the plating on the mating connector for reliable operation.